Xiaojie Xue

Mid-infrared supercontinuum generation spanning 2.0 to 15.1 μm in a chalcogenide step-index fiber.

We experimentally demonstrate mid-infrared (MIR) supercontinuum (SC) generation spanning ∼2.0 to 15.1 μm in a 3 cm-long chalcogenide step-index fiber. The pump source is generated by the difference frequency generation with a pulse width of ∼170  fs, a repetition rate of ∼1000  Hz, and a wavelength range tunable from 2.4 to 11 μm. To the best of our knowledge, this is the broadest MIR SC generation observed so far in optical fibers. It facilitates fiber-based applications in sensing, medical, and biological imaging areas.

Size-dependent upconversion luminescence and quenching mechanism of LiYF 4 : Er 3+ /Yb 3+ nanocrystals with oleate ligand adsorbed

Er3+/Yb3+ co-doped LiYF4 nanocrystals were prepared by a facile solvothermal method. By adjusting the LiOH concentration, LiYF4 crystals with the size range from 16 nm to 2.0 μm were synthesized. Under the excitation by a 976 nm laser, upconversion quantum efficiency of the LiYF4: Er3+/Yb3+ samples were measured. It was observed that upconversion quantum efficiency tended to decrease with the reduction of particle size from microscale to nanoscale. A model was proposed to clarify the surface quenching mechanism influencing the size-dependent upconversion luminescence.

Fabrication and characterization of a hybrid four-hole AsSe 2 -As 2 S 5 microstructured optical fiber with a large refractive index difference

A hybrid four-hole AsSe2-As2S5 microstructured optical fiber (MOF) with a large refractive index difference is fabricated by the rod-in-tube drawing technique. The core and the cladding are made from the AsSe2 glass and As2S5 glass, respectively. The propagation loss is ~1.8 dB/m and the nonlinear coefficient is ~2.03 × 10(4) km(-1)W(-1) at 2000 nm. Raman scattering is observed in the normal dispersion regime when the fiber is pumped by a 2 μm mode-locked picosecond fiber laser. Additionally, soliton is generated in the anomalous dispersion regime when the fiber is pumped by an optical parametric oscillator (OPO) at the pump wavelength of ~3000 nm.

Broadband cascaded four-wave mixing and supercontinuum generation in a tellurite microstructured optical fiber pumped at 2 μm

We demonstrate the broadband cascaded four-wave mixing (FWM) and supercontinuum (SC) generation in a tellurite MOF which is made from 76.5TeO(2)-6ZnO-11.5Li(2)O-6Bi(2)O(3) (TZLB, mol%) glass. By using a 2-μm picosecond laser with the center wavelength of ~1958 nm as the pump source, the broadband FWM with the frequency separation of ~1.1 THz is obtained. The bandwidth of the frequency comb spans a range of ~630 nm from ~1620 to 2250 nm at the average pump power of ~125 mW. With the average pump power increasing to ~800 mW, the broadband mid-infrared SC generation with the spectrum from ~900 to 3900 nm is observed. Changing the pump source to a femtosecond laser (optical parametric oscillator, OPO) with the center wavelength of ~2000 nm, solitons and dispersive waves (DWs) are obtained.

Mid-infrared supercontinuum generation in a novel AsSe 2 -As 2 S 5 hybrid microstructured optical fiber

A four-hole AsSe₂-As₂S₅ hybrid microstructured optical fiber (HMOF) with a large refractive index difference is fabricated by the rod-in-tube drawing technique. The core and the cladding are made from the AsSe₂ glass and As₂S₅ glass, respectively. The propagation loss is ~1.2 dB/m and the nonlinear coefficient is ~4.937×10⁴ km^-1W^-1 at ~3000 nm. Zero dispersion wavelength (ZDW) of the HMOF is ~3380 nm. Supercontinuum (SC) generation in the HMOF is investigated by pumping a 2 cm-long AsSe₂-As₂S₅ HMOF with the wavelengths of ~3062, 3241 and 3389 nm from a tunable optical parametric oscillator (OPO) system. Broadband mid-infrared SC generation with the spectrum from ~1256 to 6385 nm is obtained with the peak power of ~1337 kW at the wavelength of ~3389 nm.

Ultrabroad supercontinuum generation through filamentation in tellurite glass

Although soft glass such as tellurite or chalcogenide glass is transparent in the range of 3–6 μm, fiber made of it is difficult to generate as a supercontinuum (SC) to that range because of the high loss, the wavelength limit of the pump source, and the challenges in light-coupling. To circumvent these problems, we developed an SC light source by using tellurite bulk glass through filamentation. For this scheme, the optical path length in the glass is very short due to the adopted high pump power, so the negative influence of material loss is reduced greatly. The light-coupling is straightforward, and the coupling efficiency is high. The bulk glass for SC generation is cheap, and can be fabricated easily. We have shown that under suitable pump conditions, the SC generation by filamentation can cover from visible to 6 μm. It is the broadest SC generation by tellurite (including glass and fiber). For suitable pump conditions, the glass was free of optical breakdown. If the interface reflections were deducted, the SC conversion efficiency was 87%; the SC conversion efficiency was stable. To the best of our knowledge, this is the first report on filamentation in tellurite glass which has a comparatively small bandgap.

Five-Octave-Spanning Supercontinuum Generation in Fluoride Glass

An ultra-broadband supercontinuum (SC) covering 0.2–8.0 µm which is more than 5 octaves, is demonstrated in a piece of fluoride glass. The 20 dB bandwidth spans from 0.39 to 7.4 µm. The filaments, bright conic visible emission, and interference fringe pattern are observed. The glass thickness, optical path, and pump conditions are optimized to enable the SC to cover the entire transmission range of the glass, which includes the whole functional group region of chemical bands and groups. The SC conversion efficiency is confirmed to be stable.

Intense Ultraviolet and Blue Upconverison Emissions in Tb3+/Yb3+ Codoped KY3F10 Nanocrystals

Tb3+/Yb3+ codoped KY3F10 nanocrystals with the average size of 45 nm were synthesized using a facile hydrothermal method. Under the excitation by a 976 nm laser, the codoped samples exhibited intense ultraviolet (5D3 → 7F6) and blue upconversion emissions (5D3 → 7F5) from Tb3+ ions. It was observed for the first time that the intense ultraviolet emission was two times stronger than the green emission of Tb3+, which was about 100 times stronger than the results previously reported. The upconversion mechanism was investigated based on the energy transfer from Yb3+ to Tb3+ and the cross-relaxation process between Tb3+ pairs.

Highly Efficient Tunable Dispersive Wave in a Tellurite Microstructured Optical Fiber

We demonstrate a highly efficient, stable, and tunable dispersive wave (DW) emitted by the soliton in a tellurite microstructured optical fiber. The dependence of the generated DW properties on the average pump power is experimentally investigated. By using the 80-MHz pulse emitted from an optical parametric oscillator as the pump source, the DW from ~1626 to 1685 nm is obtained with the average pump power changing from ~250 to 440 mW at the pump wavelength of ~1760 nm. The conversion efficiency is over ~65%. The full width at half maximum (FWHM) of DW pulse at the center wavelength of 1626 nm is ~90 fs, which was measured by an intensity autocorrelator. The stable DW pulse can be used as a near-infrared femtosecond source.

Third-harmonic generation in an elliptical-core ZBLAN fluoride fiber

We demonstrate third-harmonic generation (THG) in an elliptical-core ZrF4-BaF2-LaF3-AlF3-NaF (ZBLAN) fluoride fiber, for the first time to our best knowledge. Linearly polarized THG around 523 nm is obtained when pumped by a pulse laser at 1560 nm. The extinction ratios of average power and peak power are ~6.7 and ~6.8 dB, respectively, in a 10 m long fiber. The extinction ratios are improved to ~11.1 and ~12.6 dB, respectively, when the fiber length is cut to 35 cm. Tunable THG from 605 to 740 nm is observed when pumped by an optical parametric oscillator with the pump wavelength changed from 1800 to 2200 nm.